RFR: JDK-8317866: replace NET_SocketAvailable

[Matthias Baesken]

When doing [JDK-8317603](https://bugs.openjdk.org/browse/JDK-8317603), it became clear that NET_SocketAvailable should be replaced.

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Commit messages:
 - JDK-8317866

Changes: https://git.openjdk.org/jdk/pull/16139/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16139&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317866
  Stats: 34 lines in 4 files changed: 4 ins; 27 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16139.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16139/head:pull/16139

PR: https://git.openjdk.org/jdk/pull/16139